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What is Virtualization
Types of Virtualization
The Art of Virtualization with Free Software
Master on Free Software 2009/2010
Miguel Vidal, José Castro
{mvidal,jfcastro}@libresoft.es
GSyC/Libresoft – URJC
April 24th, 2010
Miguel Vidal, José Castro
The Art of Virtualization with Free Software
What is Virtualization
Types of Virtualization
(cc) 2010 Miguel Vidal, José Castro.
Some rights reserved. This work is licensed under a Creative Commons
Attribution-Share Alike 3.0 License, available at
http://creativecommons.org/licenses/by-sa/3.0/
Miguel Vidal, José Castro
The Art of Virtualization with Free Software
What is Virtualization
Types of Virtualization
Agenda
Part 1: What is Virtualization
Part 2: Types of Virtualization
Miguel Vidal, José Castro
The Art of Virtualization with Free Software
What is Virtualization
Types of Virtualization
What is Virtualization
Miguel Vidal, José Castro
The Art of Virtualization with Free Software
What is Virtualization
Types of Virtualization
What is Virtualization
Hardware/software combination, which allows a computer to act as
several ones.
It includes making a single physical resource (such as a server, an
operating system, or storage device) appears to function as
multiple logical resources.
Miguel Vidal, José Castro
The Art of Virtualization with Free Software
What is Virtualization
Types of Virtualization
Definitions
Virtualization is a methodology of dividing the resources of a
computer into multiple execution environments.
Virtualization applies one or more concepts or technologies
such as partitioning, time-sharing, partial or complete machine
simulation, emulation, quality of service, and many others.
Colloquially, virtualization refers to the abstraction of
computer resources.
Miguel Vidal, José Castro
The Art of Virtualization with Free Software
What is Virtualization
Types of Virtualization
Hypervisors
In modern computing, Virtual Machine Monitors (aka
hypervisors) allow many different OS, tasks and software
configurations exist on the same physical machine.
The hypervisor abstracts the physical resources of the host
computer into discrete “virtual machines”.
Hypervisors ensure some level of isolation between guests.
Hypervisors also provide a uniform interface to the hardware.
Miguel Vidal, José Castro
The Art of Virtualization with Free Software
What is Virtualization
Types of Virtualization
More on hypervisors
We have two hypervisor classes:
Type 1 (or “native”, “bare-metal”): the hypervisor is a layer
between hardware and all OS. The “host OS” is known as
Control Domain, and runs over the hypervisor.
Type 2 (or “hosted”) the hypervisor is a software layer
running over the host OS.
Miguel Vidal, José Castro
The Art of Virtualization with Free Software
What is Virtualization
Types of Virtualization
History: Origins
The term “virtualization” was coined in the 1960s, to refer to
a virtual machine (sometimes called “pseudo machine”).
M44/44X Project (mid 1960s): the goal being to evaluate the
then emerging time sharing system concepts.
The architecture was based on virtual machines: the main
machine was an IBM 7044 (M44) and each virtual machine
was an experimental image of the main machine (44X).
A number of IBM-based virtual machine systems were
developed: the CP-40, the CP-67, the famous VM/370, and
many more.
A component called the virtual machine monitor (VMM) ran
directly on “real” hardware.
Multiple virtual machines could then be created via the VMM,
and each instance could run its own operating system.
Miguel Vidal, José Castro
The Art of Virtualization with Free Software
What is Virtualization
Types of Virtualization
Virtualization Extensions for x86
Since 2005, Intel and AMD have added additional hardware
support to virtualization.
Intel Virtualization Technology (VT) codename Vanderpool
AMD Virtualization (AMD-V) codename Pacifica
Added explicit funtionality to enable higher performance
hypervisors for full virtualization.
Full virtualization is easier to implement.
Xen uses theses hardware extensions to support full
virtualization.
Miguel Vidal, José Castro
The Art of Virtualization with Free Software
What is Virtualization
Types of Virtualization
Reasons for virtualization
Isolate different applications and users on the same machine
from interfering from each other.
Server environment: consolidate many servers/services on a
single machine (email, web, dns, etc.).
Run operating system or other software built for one type of
CPU on another kind of CPU.
Easily and safely test software: debugging, developing, isolated
–“sandboxed”– environments to study viruses, worms, etc.
Easily deploy software using virtual software appliances. From
business perspective, it provides a reduced total cost of
ownership (TCO)
Decrease power conssumption and cooling infraestructure in
very dense datacenters.
Miguel Vidal, José Castro
The Art of Virtualization with Free Software
What is Virtualization
Types of Virtualization
Basic concepts
The native Operating System running the virtualization
software is called the Host.
The host has control of the real hardware.
The virtualized OS is called a Guest.
There can be many Guests on a single Host.
Guests must not interfere with each other or the host.
Miguel Vidal, José Castro
The Art of Virtualization with Free Software
What is Virtualization
Types of Virtualization
Virtualization concepts
The virtualization software is called:
Hypervisor.
Virtual Machine Manager or VMM.
The VMM or Hypervisor is running as part of the host OS (or
it’s the host).
A virtual hardware instance is called a Virtual Machine or VM.
The Guests OS run inside a VM.
Miguel Vidal, José Castro
The Art of Virtualization with Free Software
What is Virtualization
Types of Virtualization
Virtualization and Cloud Computing
Cloud Computing is not the same as virtualization
management.
But most Cloud Computing deployments depend on
virtualization.
Hardware management is highly abstracted from the buyer.
Infrastructure capacity on CC is highly elastic (up or down).
Clouds are hardware-based resources converted into a “resource
pool”.
Miguel Vidal, José Castro
The Art of Virtualization with Free Software
What is Virtualization
Types of Virtualization
Types of Virtualization
Miguel Vidal, José Castro
The Art of Virtualization with Free Software
What is Virtualization
Types of Virtualization
Types of Virtualization
Create the illusion of separate hardware and complete standalone
systems. There are 4 major approaches in modern computing:
1
Emulation
2
Full virtualization
3
Paravirtualization
4
Operating system-level virtualization
Miguel Vidal, José Castro
The Art of Virtualization with Free Software
What is Virtualization
Types of Virtualization
Emulation
Virtual machine simulates the entire hardware.
Unmodified guests in different hardware architecture runs
inside a VM.
Is used to create new OS or microcode for new hardware
designs before HW is physically available.
Advantages: Simulates hardware that is not phisically
available
Caveats: Low performance and low density (high cost)
Example: basilisk II, a Mac (m68k) emulator for x86.
Miguel Vidal, José Castro
The Art of Virtualization with Free Software
What is Virtualization
Types of Virtualization
Full virtualization
Similar to emulation, unmodified guests.
Differs from emulation in that OSs are designed to run on the
same architecture as the host.
Hardware combined: CMT, Intel VT, AMD V, these CPUs
control access to privileged instructions.
Advantages: Flexibility, run different OSs from multiple
vendors.
Caveats: We can’t emulate other archs.; Performance.
Examples: VirtualBox, Xen + Intel VT.
Miguel Vidal, José Castro
The Art of Virtualization with Free Software
What is Virtualization
Types of Virtualization
Paravirtualization
Hypervisor exports a modified version of the host.
Exported VM is of the same architecture as the host.
Advantages: Performance (lightweight and fast), scalability
and manageability; strong isolation; allow virtualizing without
need special CPU.
Caveats: For same architecture. Requires porting Guest OS.
Example: Xen with standard CPU.
Miguel Vidal, José Castro
The Art of Virtualization with Free Software
What is Virtualization
Types of Virtualization
Operating system-level virtualization
Also called lightweight virtualization or paenevirtualization
(i.e. “almost virtualization”)
Virtualization is done within a traditional single OS image (no
hypervisor).
OS is modified to allow various user space server processes in
isolation from one another.
Advantages: Fast, lightweight virtualization layer. Close to
native performance. Density.
Caveats: Strong isolation is difficult to implement.
Examples: Linux VServers, FreeBSD jails, OpenSolaris
Zones/Containers
Miguel Vidal, José Castro
The Art of Virtualization with Free Software
What is Virtualization
Types of Virtualization
Others types of Virtualization
Library virtualization: Wine library (subset of the Win32
API to allow execute Windows applications)
Application virtualization (managed runtime): virtual
execution environment (standard API for cross-platform
execution). Example: Java Virtual Machine.
Advantages: Increases portability of apps.
Caveats: Slower than native code, not capable of exucting a
full operating systems
Miguel Vidal, José Castro
The Art of Virtualization with Free Software
What is Virtualization
Types of Virtualization
Desktop virtualization
Decoupling of a users physical machine from the desktop and
software he/she uses to work.
It emulates the PC hardware environment of the client and
run a virtual machine alongside the existing operating system
located on the local machine or delivered to a thin client from
a data server.
Desktops as a service: transforming desktops into a cloud
service.
Different approaches.
Citrix XenDesktop, Sun VDI, VMWare View.
Miguel Vidal, José Castro
The Art of Virtualization with Free Software
What is Virtualization
Types of Virtualization
Desktop virtualization: Advantages
Instant provisioning of new desktops.
Desktop computing power on demand.
Significant reduction in the cost of new application
deployment.
Near-zero downtime in the event of hardware failures.
Ability to access the users’ enterprise desktop environment
from any location.
Miguel Vidal, José Castro
The Art of Virtualization with Free Software
What is Virtualization
Types of Virtualization
Xen: Features
Xen uses paravirtualization, meaning that the guest operating
system must be modified to use an hypervisor.
Also allowing hardware-assisted virtualization (Intel VT or
AMD-V), for unmodified guests: a significant development
because it allows proprietary operating systems (such as
Microsoft Windows) to be virtualized.
Virtual machine migration.
On x86, the Xen host kernel code runs in protection Ring 0,
while the hosted domains run in Ring 1 or in Ring 3 (Rings:
hierarchical protection domains)
Miguel Vidal, José Castro
The Art of Virtualization with Free Software
What is Virtualization
Types of Virtualization
Xen: Benefits
Independence between virtualized systems. You can restart,
and create independently.
Better utilization of hardware of the machine: balancing
resources. A virtual machine can get more resources if needed
instead the other VM.
Easy to backup, only with a copy of the virtual machine, it can
be booted on a new server. Also, Xen allows hot migration,
providing flexibility and little recovery time before an incident.
You can modify parameters such as RAM, number of CPUs,
disk space ... to solve the needs of the virtual machine.
Test and Development Environments: multiple virtual
machines on a single physical server for testing and
development on a single machine simultaneously.
Miguel Vidal, José Castro
The Art of Virtualization with Free Software
What is Virtualization
Types of Virtualization
How does it work?
Miguel Vidal, José Castro
The Art of Virtualization with Free Software
What is Virtualization
Types of Virtualization
Kernel-based Virtual Machine (KVM)
KVM is a Linux kernel virtualization infrastructure.
Native virtualization using Intel VT or AMD-V.
First version was included in Linux 2.6.20 (February 2007).
A wide variety of guest operating systems work with KVM:
Linux, BSD, Solaris, Windows, Haiku, ReactOS and a patched
version of KVM is able to run Mac OS X.
It does not perform any emulation: a user-space program
(Qemu) uses the /dev/kvm interface to set up the guest VM’s
address space.
Miguel Vidal, José Castro
The Art of Virtualization with Free Software
What is Virtualization
Types of Virtualization
OpenSolaris xVM projects
VirtualBox: VMs for all. Cross-platform.
xVM server: Xen on Opensolaris 2009.06.
Logical domains (LDOMs): Type 1 hypervisor, “full”, for
Sparc platform.
Zones: Lightweight virtualization for OpenSolaris.
Other: Sun xVM Ops center, Sun xVM VDI.
Miguel Vidal, José Castro
The Art of Virtualization with Free Software
What is Virtualization
Types of Virtualization
Containers and zones
Virtualization which executes several instances of same
operating system (and same kernel).
Global Zone vs. local zones: we can’t exit to the global
filesystem (advanced chroot)
Without hypervisor nor virtual hardware.
Provisioning and administration very simple.
x86: with “branding” support.
From 2005 is part of Solaris 10 (and OpenSolaris).
Similar to FreeBSD jails, OpenVZ (Linux containers) or
Linux-VServer.
Miguel Vidal, José Castro
The Art of Virtualization with Free Software
What is Virtualization
Types of Virtualization
LDOMs virtualization
“Full virtualization”, Type 1 hypervisor based.
It requires special CPUs (Chip Multithreading = CMT).
Each domain is a full virtual machine with a reconfigurable
subset of hardware resources.
Operating systems running inside Logical Domains can be
started, stopped, and rebooted independently.
Base OS: Solaris 10 / Opensolaris 2009.06
Virtual machine OS: Solaris 10, Opensolaris 2009.06, Sparc
Linux, and other OS which support this architecture.
But for now, only SunOS is supported.
Miguel Vidal, José Castro
The Art of Virtualization with Free Software
What is Virtualization
Types of Virtualization
Chip Multithreading (CMT)
UltraSparc T1 / T2.
Multithread. A thread is similar to a CPU.
Example: T1 has 8 cores with 4 threads/core.
Direct SSL support on hardware (1 MAU/core).
LDOMs can assign cores to VMs.
Hypervisor runs on server firmware.
Free/Open Hardware: http://www.opensparc.net
Sun Fire T / Enterprise T / Blade T servers.
Miguel Vidal, José Castro
The Art of Virtualization with Free Software
What is Virtualization
Types of Virtualization
References
Amit Singh “An Introduction to Virtualization” (2004):
http://www.kernelthread.com/publications/
virtualization/
Comparison of platform virtual machines:
http://en.wikipedia.org/wiki/
Comparison of platform virtual machines
Jeanne Matthews et al. Running Xen. Prentice Hall, 2008
(Chapter 1: “Background and Virtualization Basics”)
Miguel Vidal, José Castro
The Art of Virtualization with Free Software